Uranium taken by Royal Navy vessel (3)
I believe the answer is:
urn
'vessel' is the definition.
(urn is a type of container)
'uranium taken by royal navy' is the wordplay.
'uranium' becomes 'U' (U is the chemical symbol for uranium).
'taken by' means one lot of letters go next to another.
'royal navy' becomes 'RN' (abbreviation for Royal Navy).
'u'+'rn'='URN'
(Other definitions for urn that I've seen before include "A vase, as for holding human ashes" , "A large vase as for human ashes" , "Large ornamental vase" , "Pot for human ashes" , "Vessel for making hot drinks" .)